A coating material, for example, metal vapor, may be coated on a surface of a steel strip through various well-known methods such as a deposition method in which a coating material is coated on a substrate, e.g., a continuous (high-speed) proceeding steel strip in a vacuum. In vacuum deposition, a solid or liquid coating material (e.g., a metal or coating material) is heated and evaporated through various methods in a vacuum and is converted into a vaporous (gaseous) state. Thus, the solid or liquid coating material having the vaporous (gaseous) state is deposited on the steel strip to form a thin film.
The continuous coating of the substrate (e.g., steel strip) through vacuum deposition may be classified according to heating method. Representative examples of continuous coating may include thermal evaporation and electron beam evaporation. Studies with respect to electro-magnetic levitation evaporation for realizing high-speed deposition have been undertaken in recent years.
In electro-magnetic levitation evaporation, a coating material is surrounded by an electro-magnetic coil, and a high frequency AC current generated by high frequency power is applied to the electro-magnetic coil. Here, the coating material is heated by the generated electro-magnetic fields to allow the coating material to be levitated. Thus, a relatively large amount of metal vapor may be deposited and coated on the surface of the steel strip, continuously moved at a high speed, with reduced heat loss when compared metal vapor generated in an existing crucible.
FIG. 1 illustrates a dry (continuous) coating apparatus using an electro-magnetic coil disclosed in Korean patent application No. 2009-0095597 filed by the same applicant of this application.
Referring to FIG. 1, in a dry coating apparatus 100 according to a related art, an electro-magnetic coil 130 for levitating and heating a coating material 112 is disposed in a vacuum V within a chamber 120 through which a substrate (e.g., a steel strip) 110 continuously passes. In addition, the solid or liquid coating material 112 supplied through a supply unit (not shown) is levitated and heated by electro-magnetic force generated in the electro-magnetic coil 130 when a high frequency current is applied thereto, thereby generating a deposition vapor (hereinafter, referred to as “metal vapor”) 114.
Here, the metal vapor 114, generated while the coating material 112 is levitated and heated, is injected onto the substrate 110 through a vapor inducing unit 140 and a vapor injection unit 150 to perform dry coating.
However, in case of the related art dry coating apparatus 100 disclosed in the above-described patent application, since a coating material to be coated on a substrate is substantially evaporated and disposed in the chamber 120 having the vacuum V and including a steel strip transfer roll 122, there is a limitation that an arcing may occur between the electro-magnetic coils 130, i.e., between turning portions of a winding part 130a or between the electro-magnetic coil 130 and an external conductor due to a high frequency AC current applied to the electro-magnetic coils 130 as shown in FIG. 2.
Thus, in the case of the related art dry coating apparatus 100, to prevent an arcing when the high frequency AC current is applied thereto while in the vacuum V, an insulation structure surrounding the electro-magnetic coil is required. Thus, there is a limitation that the dry coating apparatus 100 has a complicated structure.
For example, an insulation structure for preventing arcing by the electro-magnetic coil (i.e., a high frequency coil) 130 is disclosed in Korean patent application No. 2009-0088117 filed by the same applicant of this application.
Referring to FIG. 2, an insulator 210 surrounds the outside (the winding part 130a) of the electro-magnetic coil (the high frequency coil) 130 used in the related art dry coating apparatus 100 and a castable or a filler 220 for a ceramic is filled in the electro-magnetic coil 130 to realize an insulation structure 200.
Thus, in the case of the related art dry coating apparatus 100, a separate insulation structure for preventing an arcing in the electro-magnetic coil is required. Accordingly, there are limitations that the apparatus is complicated due to component construction and also cost for constructing and maintaining the equipment increase.
In the related art electro-magnetic coil having the insulation structure for preventing the arcing, since vibration occurs at the coil winding part 130a when a high frequency power is applied, cracks may occur in the insulation structure 200. As a result, arcing may occur at the cracked portions.
Specifically, when the high frequency current is applied to the electro-magnetic coil in the vacuum to perform high-speed coating, the vibration of the coil winding part 130a significantly increases, to potentially cause serious cracks. Thus, since the possibility of the arcing increases, the high-speed coating may be limited.
In addition, since a large amount of heat is generated in the electro-magnetic coil itself when the high frequency current is applied to the electro-magnetic coil 130, cooling water should be circulated within the electro-magnetic coil 130 for the cooling thereof. As a result, the insulation structure 200 of the electro-magnetic coil 130 as shown in FIG. 2 may be overheated due to heat dissipation being blocked.
Also, in the related art dry coating apparatus 100 shown in FIG. 1, a feed-through 300 for stably applying the high frequency current to the coil is required in a portion of the vacuum chamber 120 through which the electro-magnetic coil 130, connected to a high frequency power source 132 disposed outside the vacuum chamber 120 to supply the high frequency current to the electro-magnetic coil 130, passes, is needed.
For example, technology with respect to the feed-through 300 of the electro-magnetic coil are disclosed in Korean patent application No. 2009-0092626 filed by the same applicant as that of this application.
In the case of the feed-through 300 disclosed in the patent application, since the feed-through 300 is provided on the assumption of the electro-magnetic coil in the vacuum, a separate feed-through part is eventually required in the related art. The feed-through may be relatively expensive and have a complicated structure.
Thus, in the related art dry coating apparatus 100, since at least a wound portion of the electro-magnetic coil for substantially levitating and heating the coating material to generate metal vapor is disposed in the vacuum, the separate components such as the insulation structure 200 or the feed-through 300 are necessarily required, as described above. Thus, the overall structure of the apparatus may be complicated. In addition, due to the heat generation in the electro-magnetic coil and the vibration in the coil winding part, it is difficult to apply the high frequency current. Therefore, it may be difficult to realize the high-speed coating.
An aspect of the present invention provides a dry coating apparatus in which an electro-magnetic coil that is a heating source is disposed in the atmosphere to remove the possibility of an arcing due to an existing electro-magnetic coil in a vacuum and to omit related components, thereby improve operation stability of the apparatus, and also, a simplified structure is enable and metal vapor generation capacity increases to realize high-speed coating, thereby improving productivity and reducing power consumption.